Method for transmitting control information, and method for generating codeword for the same

ABSTRACT

A method for transmitting downlink control information and a method for generating a codeword for the same are disclosed. In generating a long code having a low code rate, a basic code of which minimum distance between codes is maximized is repeated by a prescribed number of times and bits of the repeated code are adjusted. Therefore, a minimum distance condition between codes of a long code is satisfied and simultaneously the code can be simply generated. Furthermore, control information can be transmitted with a low error rate by using the generated code.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application also claims the benefit of U.S. Provisional ApplicationSer. No. 60/917,161, filed on May 10, 2007 and 60/943,293, filed on Jun.11, 2007, the contents of which are hereby incorporated by referenceherein in their entirety.

This application claims the benefit of the Korean Patent Application No.10-2007-0107595, filed on Oct. 25, 2007, which is hereby incorporated byreference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for transmitting downlinkcontrol information and a method for generating a codeword for the same.

2. Discussion of the Related Art

Among fundamentals of basic code theories, a few things necessary for adescription of the present invention will now be explained.

When a typical binary error correction code is represented as [n, k, d],‘n’ means the number of bits of an encoded codeword, ‘k’ means thenumber of information bits before encoding, and ‘d’ means a minimumvalue among distances between codewords. Here, since the codeword is abinary code, the length of the codeword is 2^(n) and the total number ofthe encoded codewords is 2^(k). On the other hand, the binary errorcorrection code may be simply expressed as an [n, k] code forconvenience.

Hereinafter, ‘n’, ‘k’ and ‘d’ will have the abovementioned meaningsunless otherwise stated.

A code rate R is defined as a value dividing the number of informationbits by the number of bits of a codeword (i.e., R=k/n).

A Hamming distance is the number of bits of which corresponding bitvalues are different in binary codes having the same number of bits. Ifa Hamming distance ‘d’ is equal to or greater than (2a+1), errors asmany as ‘a’ can be corrected. For example, two codewords are ‘101011’and ‘110010’, a Hamming distance between the two codewords is 3 and oneerror can be corrected.

A minimum value among distances between any two codewords belonging to acode is defined as a minimum distance. The minimum distance is one ofimportant metrics to evaluate performance of a code. The aforementionedHamming distance can be used as a distance between two codewords. As adistance between codewords generated through an encoding process becomesgreater, since the probability that a corresponding codeword is judgedto be a different codeword becomes lower, encoding performance isincreased. The performance of a code is determined by a distance betweencodewords having the worst performance, i.e., a minimum distance betweencodewords. Consequently, a code in which minimum distance is maximizedshows good performance.

Meanwhile, a 3GPP LTE (3rd Generation Partnership Project Long TermEvolution) system has proposed that information indicating a format of acontrol channel during transmission of control information betransmitted through a physical control format indicator channel(“PCFICH”). The PCFICH demands to transmit a code having a very low coderate to minimize an occurrence of an error during transmission sinceinformation on a format transmitting control information is transmittedtherethrough.

However, in generating a long-length code having a very low code rate,it is difficult to set a minimum distance between codewords to a maximumvalue.

SUMMARY OF THE INVENTION

An object of the present invention devised to solve the problem providesa method for constructing a code such that a minimum distance betweencodes is maximized and simultaneously generating a long-length codehaving a low code rate and a method for transmitting a control signalusing the same.

For this end, a long-length code is generated by repeating a basic code.When a code of a predetermined length can not be generated by simplyrepeating the basic code, an appropriate adjustment is performed togenerate the code having the predetermined length while satisfying acondition that a minimum distance between codes is maximized.

Another object of the present invention provides a method fortransmitting downlink control information using a code generated by theabove-described method.

The object of the present invention can be achieved by providing amethod for transmitting control information through a downlink by asystem. The method includes: transmitting the control informationthrough a downlink control channel; and transmitting information on thenumber of OFDM (orthogonal frequency division multiplexing) symbolsoccupied by the control information on the downlink control channel byusing a prescribed code, wherein the prescribed code is one of

(0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1, 1,0,1),

)1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0, 1,1,0),

(1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1, 0,1,1), and

(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0),according to information on the number of OFDM symbols occupied by thecontrol information.

The information on the number of OFDM symbols occupied by the controlinformation on the downlink control channel may be a control formatindicator (CFI), and the information on the number of OFDM symbolsoccupied by the control information on the downlink control channel maybe transmitted through a physical control format indicator channel(PCFICH).

The prescribed code may be

(0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0, 1,1,0,1) whenthe number of OFDM symbols occupied by the control information is 1,

(1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1, 0,1,1,0) whenthe number of OFDM symbols occupied by the control information is 2, and

(1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1, 1,0,1,1) whenthe number of OFDM symbols occupied by the control information is 3.

In another aspect of the present invention, provided herein is a methodfor receiving control information through a downlink by a User Equipment(UE). The method includes: receiving information on the number of OFDMsymbols occupied by the control information on a downlink controlchannel by using a prescribed code; and receiving the controlinformation through the downlink control channel by using the prescribedcode, wherein the prescribed code is one of

(0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0, 1,1,0,1),

(1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1, 0,1,1,0),

(1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1, 1,0,1,1), and

(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0),according to the number of OFDM symbols occupied by the controlinformation.

In a further aspect of the present invention, provided herein is amethod for generating a codeword. The method includes: acquiringinformation on the number of OFDM symbols occupied by controlinformation on a downlink control channel; and generating the codewordaccording to the acquired information, wherein the codeword is generatedby repeating any one of simplex codes (0, 1, 1), (1, 0, 1), (1, 1, 0),and (0, 0, 0) by 11 times and puncturing the last one bit.

In still another aspect of the present invention, provided herein is amethod for generating a codeword. The method includes: acquiringinformation on the number of OFDM symbols occupied by controlinformation on a downlink control channel; and generating the codewordaccording to the acquired information, wherein the codeword is generatedby repeating any one of simplex codes (0, 1, 1), (1, 0, 1), (1, 1, 0),and (0, 0, 0) by 9 times and inserting any one of Hamming codes (0, 1,1, 0, 1), (1, 0, 1, 1, 0), (1, 1, 0, 1, 1), and (0, 0, 0, 0, 0).

In still yet another aspect of the present invention, provided herein isa method for generating a codeword. The method includes: acquiringinformation on the number of OFDM symbols occupied by controlinformation on a downlink control channel; and generating the codewordaccording to the acquired information, wherein the acquired informationis expressed as 2 information bits, and the codeword is generated byrepeating any one of simplex codes (0, 1, 1), (1, 0, 1), (1, 1, 0), and(0, 0, 0) by 10 times and inserting the information bits.

According to the aspects of the present invention, a long code having alow code rate can be generated by a simple method while a minimumdistance between codes is maximized.

Moreover, control information can be transmitted with a low error rateby representing information on the number of OFDM symbols occupied bythe control information using the generated code.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a diagram for explaining a process of generating a long-lengthcode having a low code rate according to an exemplary embodiment of thepresent invention.

FIG. 2 is a flow chart schematically illustrating a process ofgenerating a long-length code having a low code rate according to anexemplary embodiment of the present invention.

FIGS. 3A to 3C are diagrams for explaining a relationship between apuncturing position of a simplex code and an information bit accordingto an exemplary embodiment of the present invention.

FIGS. 4A to 4C are diagrams for explaining examples of row or columnconversion of a basic code in terms of mapping with an information bitaccording to an exemplary embodiment of the present invention.

FIGS. 5A and 5B are diagrams for explaining a process of transmittingcontrol information using a [32,2] code according to an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the annexed drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention.

The following description provides specific details for a thoroughunderstanding of embodiments of the invention. However, one skilled inthe art will understand that the invention may be practiced withoutthese details. In other instances, well-known structures and functionshave not been described in detail or may be shown in block diagram formto avoid unnecessarily obscuring the description of embodiments of theinvention. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

In generating a long code having a low code rate, there are provided amethod for constructing a code such that a minimum distance betweencodes is maximized and simultaneously generating the long code by asimple method and a method for transmitting a control signal using thesame. For this end, a condition that a minimum distance between codes ismaximized will be considered in detail.

In the following description of the present invention, a concept of anormalized minimum distance is introduced as a method for comparingvarious coding techniques. Namely, in a binary error correction code [n,k, d], a value dividing a minimum distance ‘d’ by the number ‘n’ of bitsof a codeword is defined as the normalized minimum distance and thenormalized minimum distance is expressed as {circumflex over (d)} forconvenience of description.

That is, the normalized minimum distance can be expressed as follows.

$\begin{matrix}{\hat{d} = \frac{d}{n}} & \lbrack {{Equation}\mspace{20mu} 1} \rbrack\end{matrix}$

Hereinafter, the Plotkin bound will be explained to consider conditionsfor setting a minimum distance between codes to a maximum value. Adetailed description of the Plotkin bound is disclosed in detail in“John G. Proakis, Wiley Encyclopedia of Telecommunications, WileyInterscience, New Jersey, 2003, vol. 2, pp 929-935”.

The Plotkin bound is summarized in brief as follows.

When a general binary error correction code is expressed as [n, k, d],‘n’ means the number of bits of a encoded codeword, ‘k’ means the numberof information bits before encoding, and ‘d’ means a minimum value amongdistances between codewords. The above-described Plotkin bound can beexpressed as follows.

$\begin{matrix}\{ \begin{matrix}{2^{k} \leq {2( \frac{d}{{2d} - n} )}} & {{{{if}\mspace{14mu} d} = {even}},} & {d > \frac{n}{2}} \\{2^{k} \leq {4d}} & {{{{if}\mspace{14mu} d} = {even}},} & {d = \frac{n}{2}} \\{2^{k} \leq {2( \frac{d + 1}{{2d} + 1 - n} )}} & {{{{if}\mspace{14mu} d} = {odd}},} & {d > \frac{n - 1}{2}} \\{2^{k} \leq {4( {d + 1} )}} & {{{{if}\mspace{14mu} d} = {odd}},} & {d = \frac{n - 1}{2}}\end{matrix}  & \lbrack {{Equation}\mspace{20mu} 2} \rbrack\end{matrix}$

Plotkin bound expressed as indicated in Equation 2 can again beexpressed based on the minimum distance d as follows.

$\begin{matrix}\{ \begin{matrix}{d \leq {n \times \frac{2^{k - 1}}{2^{k} - 1}}} & {{{{if}\mspace{14mu} d} = {even}},} & {d > \frac{n}{2}} \\{d = {\frac{n}{2} \geq 2^{k - 2}}} & {{{{if}\mspace{14mu} d} = {even}},} & {d = \frac{n}{2}} \\{d \leq {{( {n - 1} ) \times \frac{2^{k - 1}}{2^{k} - 1}} + \frac{1}{2^{k} - 1}}} & {{{{if}\mspace{14mu} d} = {odd}},} & {d > \frac{n - 1}{2}} \\{d = {\frac{n - 1}{2} \geq {2^{k - 2} - 1}}} & {{{{if}\mspace{14mu} d} = {odd}},} & {d = \frac{n - 1}{2}}\end{matrix}  & \lbrack {{Equation}\mspace{20mu} 3} \rbrack\end{matrix}$

A method for generating a code expressed generally as [n, k, d] will nowbe considered with reference to the above Equation 3 according to anexemplary embodiment of the present invention. If the minimum distance dis greater than half of a code length (i.e., d>n/2), it is desirable todesign an optimal code so as to satisfy the above-described Plotkinbound.

Here, it is assumed in the exemplary embodiment of the present inventionthat a generated code has a low code rate (i.e., n>2^(k)). When n=2^(k),an orthogonal code can be generated and a minimum distance of theorthogonal code is n/2. Therefore, it makes sense to consider only thefollowing two cases with respect to the Plotkin bound at a low code rateassumed in this exemplary embodiment of the present invention.

$\begin{matrix}\{ \begin{matrix}{d = {n \geq \frac{2^{k - 1}}{2^{k} - 1}}} & {{{{if}\mspace{14mu} d} = {even}},} & {d > \frac{n}{2}} \\{d \leq {{( {n - 1} ) \times \frac{2^{k - 1}}{2^{k} - 1}} + \frac{1}{2^{k} - 1}}} & {{{{if}\mspace{14mu} d} = {odd}},} & {d > \frac{n - 1}{2}}\end{matrix}  & \lbrack {{Equation}\mspace{20mu} 4} \rbrack\end{matrix}$

Under the above conditions indicated in Equation 4, cases where theminimum distance d is an even number and an odd number will now bedescribed.

First, assuming that the minimum distance d is an even number, a maximumvalue of the minimum distance d is

$n \times \frac{2^{k - 1}}{2^{k} - 1}$

as known from the first expression of Equation 4. When considering thenormalized minimum distance {circumflex over (d)} obtained by dividingthe minimum distance by the number of bits of a codeword, a maximumvalue of the normalized minimum distance {circumflex over (d)} is

$\frac{2^{k - 1}}{2^{k} - 1}.$

Therefore, if an entire code can be constructed by repeating a code ofwhich normalized minimum distance {circumflex over (d)} is

$\frac{2^{k - 1}}{2^{k} - 1},$

since a maximum value of a minimum distance is satisfied, theconstructed code can be an optimal code in terms of the minimumdistance.

Next, assuming that the minimum distance is an odd number, a maximumvalue of the minimum distance d is

${( {n - 1} ) \times \frac{2^{k - 1}}{2^{k} - 1}} + \frac{1}{2^{k} - 1}$

as known from the second expression of Equation 4. Then a maximum valueof the normalized minimum distance {circumflex over (d)} becomes

$\frac{2^{k - 1}}{2^{k} - 1} + {\frac{1}{2^{k} - 1}.}$

Therefore, when an entire code can be constructed by repeating a code ofwhich normalized minimum distance {circumflex over (d)} approximates to

$\frac{2^{k - 1}}{2^{k} - 1},$

a maximum value of a minimum distance is satisfied and the constructedcode becomes an optimal code in terms of the minimum distance.

An example of a code of which normalized minimum distance is

$\frac{2^{k - 1}}{2^{k} - 1}$

is a simplex code.

The simplex code has a property of [2^(k)−1, k, 2^(k-1)] and eachnormalized distance between codewords is the same as

$\frac{2^{k - 1}}{2^{k} - 1}.$

The simplex code can geometrically be represented as vertexes in a unitcube of a (2^(k)−1) dimension. A dual code of the simplex code is aHamming code having a minimum distance 3.

The simplex code is also known as a maximal length shift register code,an m-sequence, or a Pseudo-random noise (PN) sequence. When a code is abinary code expressed as +1 and −1 and the number of codewords is M, acorrelation function between different codewords is the same as −1/(M−1)(where M is an even number) or −1/M (where M is an odd number). In thesimplex code, a maximum correlation function between different codewordsamong binary codes of the same number of codewords is minimized.

An entire code represented as [n, k, d] according to an exemplaryembodiment of the present invention is generated as follows. First, asimplex code [2^(k)−1, k, 2^(k-1)] is generated as a basic code andrepeated until an entire code length becomes n. Then a long code ofwhich normalized minimum distance is

$\frac{2^{k - 1}}{2^{k} - 1}$

can be generated.

In some cases, however, the entire code length n may not be a multipleof the basic code length 2^(k)−1. In an exemplary embodiment of thepresent invention, a method for generating a code having a length n whenthe entire code length n is not a multiple of the basic code length2^(k)−1 is proposed.

FIG. 1 is a diagram for explaining a process of generating a long-lengthcode having a low code rate according to an exemplary embodiment of thepresent invention.

As illustrated in FIG. 1, a case where a code length n is not a multipleof 2^(k)−1 is considered. Namely, it is assumed that n=m (2^(k)−1)+r(where m is the number of repetitions of a basic code).

When the above relationship is satisfied, a method for generating a codehaving a length n is proposed as follows.

First, a simplex code satisfying [2^(k)−1, k, 2^(k-1)] is generated as abasic code. Next, a code repeating the basic code as many as m times isgenerated. Finally, r bits are generated by puncturing the simplex codeor by using any other codes of which minimum distance is maximized.

As a method for generating the r bits when k is a small number, a codecapable of maximizing a minimum distance may be considered by searchingall the possible cases. A general assumption for the r bits is that r isless than a basic code length 2^(k)−1. However, r may be greater than2^(k)−1 according to a specific exemplary embodiment of the presentinvention which will be described.

After the basic code having a length 2^(k)−1 is repeated, a process foradjusting prescribed bits to generate a code having a length n may bevarious and this will be described hereinafter in detail.

The above-described code generating process will now be described indetail in terms of a minimum distance.

First, the Plotkin bound of a minimum distance at a low code rate needsto consider only the following two cases (where n=m(2^(k)−1)+r).

$\begin{matrix}\{ \begin{matrix}\begin{matrix}{{{d \leq {n \times \frac{2^{k - 1}}{2^{k} - 1}\mspace{14mu} {if}\mspace{14mu} d}} = {even}},{d > \frac{n}{2}}} \\{= {{\{ {{m( {2^{k} - 1} )} + r} \} \times \frac{2^{k - 1}}{2^{k} - 1}} = {{m \times 2^{k - 1}} + {r \times \frac{2^{k - 1}}{2^{k} - 1}}}}}\end{matrix} \\\begin{matrix}{{{d \leq {{( {n - 1} ) \times \frac{2^{k - 1}}{2^{k} - 1}} + {\frac{1}{2^{k} - 1}\mspace{14mu} {if}\mspace{14mu} d}}} = {odd}},{d > \frac{n - 1}{2}}} \\{= {{( {{m( {2^{k} - 1} )} + r - 1} ) \times \frac{2^{k - 1}}{2^{k} - 1}} + \frac{1}{2^{k} - 1}}} \\{= {{m \times 2^{k - 1}} + \frac{{( {r - 1} )2^{k - 1}} + 1}{2^{k} - 1}}}\end{matrix}\end{matrix}  & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

When a code length n (=m(2^(k)−1)+r) is not a multiple of a basic codelength, a code generating method is as follows.

That is, there are a part constructed by repeating a simplex codesatisfying [2^(k)−1, k, 2^(k-1)] by m times and an [r, k] code partobtained by adding r bits. The added [r, k] may be constructed in manyways and it is desirable to meet the next minimum distance (hereinafter,referred to as d_(r) for convenience of description) from the Plokinbound.

$\begin{matrix}{{\lbrack {r,k,d_{r}} \rbrack \mspace{14mu} \ldots \mspace{14mu} d_{r}} = \{ \begin{matrix}{\leq {r \times \frac{2^{k - 1}}{2^{k} - 1}}} & {{{{if}\mspace{14mu} d} = {even}},{d > \frac{n}{2}}} \\{\leq \frac{{( {r - 1} )2^{k - 1}} + 1}{2^{k} - 1}} & {{{{if}\mspace{14mu} d} = {odd}},{d > \frac{n - 1}{2}}}\end{matrix} } & \lbrack {{Equation}\mspace{14mu} 6} \rbrack\end{matrix}$

where d_(r) has an integral value.

The [r, k] code may be constructed in many ways, for example, bypuncturing prescribed bits in a simplex code used for repetition orusing other codes except for the simplex code. However, in adjusting rbits, it is important to generate a code approximating to the Plotkinbound for a minimum distance indicated in Equation 6.

On the other hand, a meaningful range of the value r will be consideredhereinafter.

As described above, a code having a length r may be constructed bypuncturing prescribed bits in a simplex code used for repetition orusing other codes except for the simplex code. When a code having alength r is generated by using a code different from the simplex code sothat a minimum distance between codes is maximized, there is nonecessity for limiting the value r to a specific range. In other words,the value r may be less or greater than the basic code length 2^(k)−1.If the value r is greater than 2^(k)−1, any code satisfying a conditionthat a minimum distance between codes is maximized within the Plotkinbound can be generated.

On the other hand, when a different code except for the simplex code isnot used, since the code length n is equal to m(2^(k)−1)+r, r is lessthan (2^(k)−1). Therefore, the range of r varies according to k. Thereis no need to consider a case where r is less than k. In this case,since r which is less than the number k of bits to be actuallytransmitted is used, coding performed by adding redundant bits ismeaningless. Consequently, a meaningful range of r becomes [k, 2^(k)−2]unless a code except for the simplex code is used to generate a codehaving a length r.

However, if r is equal to k (i.e., r=k), then it is desirable totransmit a given information bit (a systematic bit) to maximize aminimum distance.

Hereinafter, a method for generating a long code having a low code ratewill be described as a basic embodiment for convenience of description.

FIG. 2 is a flow chart schematically illustrating a process ofgenerating a long-length code having a low code rate according to anexemplary embodiment of the present invention.

Referring to FIG. 2, a basic code of which minimum distance betweencodes has a maximum value within the Plotkin bound is generated at stepS201. A typical code satisfying the above condition may be a simplexcode. However, if there are other codes of which minimum distancebetween codes has a maximum value within the Plotkin bound, those codesmay be used.

The basic code is repeated by m times at step S202. When a code of whichminimum distance between codes is maximized is repeated, a conditionthat the minimum distance is maximized within the Plotkin bound issatisfied like a basic code in terms of a normalized minimum distance.

However, when a code length n is not a multiple of the basic codelength, the other length r is generated in step S203. Although there maybe many methods for generating a code having a length r, it is desirableto set the code having the length r to have a minimum distance of amaximum value within the Plotkin bound in terms of the normalizedminimum distance.

For this end, prescribed bits in the basic code used for repetition arepunctured as shown in step S203-1. If the other length r is equal to thenumber of information bits, the information bit is used as the r-lengthcode as shown in step S203-2. If the length r is equal to a length ofany arbitrary code satisfying a maximum-minimum distance conditionwithin the Plotkin bound, the arbitrary code is used as the r-lengthcode as shown in step S203-3.

Hereinafter, methods for generating the r-length code according to theembodiment of the present invention, for example, a method usingpuncturing and various modifications of a code generating method will bedescribed.

Furthermore, a method for generating a [32,2] code (or (32, 2) code) byapplying the code generating method to a 3GPP LTE system, and a methodfor transmitting a control signal using the [32,2] code will bedescribed.

First, a method for generating the r-length code using puncturing willnow be described according to the embodiment of the present invention.

Method for Generating an r-Length Code Using Puncturing

An optimal code generating method using puncturing in a case where acode length n is not a multiple of (2^(k)−1) will be described indetail. First, a basic code of a short length is generated and then thebasic code is repeated so that the basic code may be greater than thecode length n. The excessive bits are punctured from the basic code. Amethod for optimally selecting a puncturing location in a puncturingprocess is proposed as follows.

In generating an [r, k] code of which minimum distance is maximizedwithin the Plotkin bound, a method for constructing a [2^(k)−1, k,2^(k-1)] simplex code using puncturing is considered. The number ofpuncturing bits is 2^(k)−1−r and a condition for determining thepuncturing locations of (2^(k)−1−r) bits is to maximally keep a minimumdistance within the Plotkin bound.

The puncturing location may be determined in various ways. As a simpleand sure example, all possible puncturing locations may be checked. Thatis, if the number (2^(k)−1−r) of puncturing locations is small and thusthe number of possible puncturing locations is small, all possible casesmay be tested. In this case, optimal puncturing locations may bedetermined by checking whether a condition that a minimum distance ismaximally maintained within the Plotkin bound is satisfied while varyingthe puncturing locations.

A fixed puncturing location may be used. If the number of puncturingbits is 2^(k)−1−r, a method for successively puncturing 2^(k)−1−r bitsfrom the first bit location is considered. In more detail, (2^(k)−1−r)bits corresponding to the number of puncturing bits are punctured fromthe first bit location from the [2^(k)−1, k, 2^(k-1)] simplex code.However, since this method can not ensure a condition that a minimumdistance is maximally maintained within the Plotkin bound, it isnecessary to check whether a code generated after puncturing meets theabove condition.

Hereinafter, whether the minimum distance condition is satisfied will bedescribed when puncturing successive bits from the first location inpuncturing a simplex code. If the code length n is m(2^(k)−1)+r, ameaningful range of r is [k, 2^(k)−2](from k to 2^(k)−2, bothinclusive).

It is assumed that k is 2. Since k is 2, r is less than 3 (=2²−1) and aneffective range of r is [2, 2](from 2 to 2, both inclusive). Therefore,only a case where r=2 is considered. In this case, original twoinformation bits are used as an r-length code and this shows the sameresult as a case where the first bit is punctured from a [3, 2, 2]simplex code.

This will be described with reference to FIGS. 3A to 3C.

FIGS. 3A to 3C are diagrams for explaining a relationship between apuncturing location of a simplex code and an information bit.

A matrix used to generate a [3, 2, 2] simplex code is illustrated inFIG. 3A. In FIG. 3B, a process for generating simplex codes (0, 0, 0),(1, 0, 1), (1, 1, 0), (0, 1, 1) with respect to information bits (0, 0),(0, 1), (1, 0), (1, 1), respectively is illustrated.

In generating the r-length code, it is effective to use only theinformation bit when r=2. This shows the same result as a case where thefirst bit of the [3, 2, 2] simplex code is punctured as shown byPuncturing (a) in FIG. 3C.

When the first bit of the [3, 2, 2] simplex code is punctured or onlythe information bit is used, the Plotkin bound can be expressed asfollows.

$\begin{matrix}{{\lbrack {2,2,d_{r}} \rbrack \mspace{14mu} \ldots \mspace{14mu} d_{r}} = \{ \begin{matrix}{{\leq {2 \times \frac{2^{2 - 1}}{2^{2} - 1}}} = \frac{4}{3}} & {{{{if}\mspace{14mu} d} = {even}},{d > \frac{n}{2}}} \\{{\leq \frac{{( {2 - 1} )2^{2 - 1}} + 1}{2^{2} - 1}} = \frac{4}{3}} & {{{{if}\mspace{14mu} d} = {odd}},{d > \frac{n - 1}{2}}}\end{matrix} } & \lbrack {{Equation}\mspace{14mu} 7} \rbrack\end{matrix}$

Under a Plotkin bound condition indicated in Equation 7, it is desirablethat an integral d_(r) satisfies a maximum value 1.

Meanwhile, when the first bit is punctured from the [3, 2, 2] simplexcode or only the information bit is used, since a minimum distancebetween codes is 1 as known from FIG. 3C, the condition that the minimumdistance is maximized within the Plotkin bound is satisfied.

Therefore, if k=2 and r=2 in generating the r-length code usingpuncturing, it is proposed that the first bit is punctured from the [3,2, 2] simplex code and this shows the same result as a case where theinformation bit is used as the r-length code.

Next, it is assumed that k=3.

If k is 3, r is less than 7 (=2³−1) and an effective range of r is [3,6] (from 3 to 6, both inclusive). Therefore, only the cases where r is3, 4, 5 and 6 are considered.

If r is 6, it is possible to generate the r-length code by puncturingthe first bit from a [7, 3, 4] simplex code. In this case, the Plotkinbound can be calculated as follows.

$\begin{matrix}{{\lbrack {6,3,d_{r}} \rbrack \mspace{14mu} \ldots \mspace{14mu} d_{r}} = \{ \begin{matrix}{{\leq {6 \times \frac{2^{3 - 1}}{2^{3} - 1}}} = \frac{24}{7}} & {{{{if}\mspace{14mu} d} = {even}},{d > \frac{n}{2}}} \\{{\leq \frac{{( {6 - 1} )2^{3 - 1}} + 1}{2^{3} - 1}} = \frac{21}{7}} & {{{{if}\mspace{14mu} d} = {odd}},{d > \frac{n - 1}{2}}}\end{matrix} } & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

Then an integral d_(r) has an upper limit of 24/7 or 21/7 and thereforea maximum integer value of d_(r) is 3.

A case where d is either an even number or an odd number is consideredfor the Plotkin bound and then the other case will be naturally derived.Hereinafter, only a case where d is an even number will be described.

When calculating a minimum distance by puncturing the first bit from the[7, 3, 4] simplex code, the minimum distance of 3 is obtained. Then itwill be understood that the Plotkin bound condition is satisfied.

Therefore, if k=3 and r=6 in generating the r-length code usingpuncturing according to the exemplary embodiment of the presentinvention, it is proposed to puncture the first bit from the [7, 3, 4]simplex code.

Next, a case where k=3 and r=5 is considered.

In this case, a method for puncturing two successive bits, that is, thefirst and second bits from the [7, 3, 4] simplex code is described. ThePlotkin bound is calculated as follows.

$\begin{matrix}{{{{\lbrack {5,3,d_{r}} \rbrack \mspace{14mu} \ldots \mspace{14mu} d_{r}} \leq {5 \times \frac{2^{3 - 1}}{2^{3} - 1}}} = {{\frac{20}{7}\mspace{14mu} {if}\mspace{14mu} d} = {even}}},{d > \frac{n}{2}}} & \lbrack {{Equation}\mspace{14mu} 9} \rbrack\end{matrix}$

As described above, since only the case where d is an even number isconsidered, a maximum value of an integral d_(r) is 2 as known fromEquation 9.

Meanwhile, since a minimum distance when the first and second bits arepunctured from the [7, 3, 4] simplex code is 2, the above Plotkin boundcondition is satisfied.

Therefore, if k=3 and r=5 in generating the r-length code usingpuncturing, it is proposed to generate the code by puncturing twosuccessive bits, that is, the first and second bits from the [7, 3, 4]simplex code.

Next, a case where k=3 and r=4 is considered.

In this case, a method for generating a code by puncturing threesuccessive bits, that is, first to third bits from the [7, 3, 4] simplexcode is considered. The Plotkin bound is calculated as follows.

$\begin{matrix}{{{{\lbrack {4,3,d_{r}} \rbrack \mspace{14mu} \ldots \mspace{14mu} d_{r}} \leq {4 \times \frac{2^{3 - 1}}{2^{3} - 1}}} = {{\frac{16}{7}\mspace{14mu} {if}\mspace{14mu} d} = {even}}},{d > \frac{n}{2}}} & \lbrack {{Equation}\mspace{14mu} 10} \rbrack\end{matrix}$

It will be understood that a maximum value of an integral d_(r) is 2from the above Equation 10.

When calculating a minimum distance by puncturing the first to thirdbits from the [7, 3, 4] simplex code, the minimum distance of 2 isobtained and the Plotkin bound condition is satisfied.

Therefore, if k=3 and r=4 in generating the r-length code usingpuncturing, it is proposed to generate a code by puncturing threesuccessive bits of the first to third bits from the [7, 3, 4] simplexcode.

Finally, a case where k=3 and r=3 is considered.

In this case, a method for generating a code by puncturing foursuccessive bits of the first to fourth bits from the [7, 3, 4] simplexcode is considered. In this case, the Plotkin bound is calculated asfollows.

$\begin{matrix}{{{{\lbrack {3,3,d_{r}} \rbrack \mspace{14mu} \ldots \mspace{14mu} d_{r}} \leq {3 \times \frac{2^{3 - 1}}{2^{3} - 1}}} = {{\frac{12}{7}\mspace{14mu} {if}\mspace{14mu} d} = {even}}},{d > \frac{n}{2}}} & \lbrack {{Equation}\mspace{14mu} 11} \rbrack\end{matrix}$

It will be understood that a maximum value of an integral d_(r) is 1from the above Equation 11.

Since a minimum distance calculated by puncturing four successive bitsfrom the [7, 3, 4] simplex code is 1, the above Plotkin bound conditionis satisfied.

The above case where r is equal to k may also be explained as the casewhere three information bits (or systematic bits) are used as ther-length code.

Therefore, if k=3 and r=3 in generating the r-length code, it isproposed to puncture four successive bits of the first to fourth bitsfrom the [7, 3, 4] simplex code or to use the information bit as ther-length code.

Methods for generating the r-length code using puncturing when k=2 andk=3 may be generalized so that the methods may be applied to cases wherek is 4 or more.

That is, even when k is 4 or more, it is possible to generate an [r, k]code by successively puncturing (2^(k)−1−r) bits from the first bitlocation from a [2^(k)−1, k, 2^(k-1)] simplex code.

Modification 1

However, the puncturing locations punctured successively from the firstbit of (2^(k)−1−r) bits do not mean the only locations which maximize aminimum distance within the Plotkin bound. In some cases, the r-lengthcode of which minimum distance is maximized within the Plotkin bound maybe generated even when corresponding bits are punctured in otherlocations.

For example, in puncturing one bit when k=2 and r=2, the last bit may bepunctured instead of the first bit so that the r-length code of whichd_(r) value becomes a maximum value within the Plotkin bound. That is,it will be appreciated that d_(r) is 1 even when a puncturing locationof one bit is the third bit as indicated by Puncturing (b) in FIG. 3C.

Modification 2

When an entire code of a simplex code of which normalized minimumdistance has a maximum value is expressed as a matrix, a characteristicof a minimum distance is not varied even though location of either a rowor a column or locations of both the row and column are permutated.

Therefore, in repeating a simplex code by m times, an optimalcharacteristic of a minimum distance is not varied even though locationsof a row and column of a code having a small length are varied.Accordingly, it is possible to obtain a desired optimal minimum distanceeven though a form of the simplex code is varied or fixed.

FIGS. 4A to 4C are diagrams for explaining examples of row or columnconversion of a simplex code in terms of mapping with an informationbit.

As described above, even if the location of a column or row of a simplexcode as a basic code used for repetition is permutated in generating ann-length code, a minimum distance characteristic is not varied. In thiscase, permutation of a column or row of the simplex code may mean that amapping relationship with an information bit is changed.

That is, when information bits (0, 1), (1, 0), (1, 1), and (0, 0) aremapped to simplex codes #1 (1, 0, 1), (1, 1, 0), (0, 1, 1), and (0, 0,0), respectively as shown in FIG. 4A, simplex codes #2 of which row ispermutated may be used instead of the simplex codes #1.

The same result may be described in another aspect as follows. Asillustrated in FIG. 4B, when the first column of the simplex codes #1 ispermutated to the third column thereof and when the second and thirdcolumns of the simplex codes #1 are permutated to the first and secondcolumns thereof, respectively, a code matrix which is the same as thesimplex codes #2 illustrated in FIG. 4A is generated.

The permutation of a column or row of the simplex code may correspond toa mapping variation between the information bit and the simplex code asillustrated in FIG. 4C. Namely, in the simplex codes #2, informationbits (0, 1), (1, 0), (1, 1), and (0, 0) are mapped to simplex codes (0,1, 1) (1, 0, 1), (1, 1, 0), and (0, 0, 0), respectively.

Modification 3

Codes of which minimum distance is maximized may be modified in variousways.

First, since a distance between codes is not varied even when 0 and 1are interchanged, a code may be modified by interchanging 0 and 1 of agenerated code.

Second, when an entire code is expressed in a matrix so that each codeoccupies each row of the matrix, a minimum distance characteristic isnot varied even though the location of a column or a row or locations ofthe column and row are permutated. Therefore, it is possible to change acode by exchanging either a column or row or both the column and row ofa code matrix of a previously generated code.

In the above description, when the length of an entire code is not amultiple of a basic code in generating a long-length code having a lowcode rate by using the basic code having a minimum distancecharacteristic, methods for adjusting the other length part and variousmodifications of these methods have been considered.

Hereinafter, an example of applying the above code generating methods toa 3GPP LTE system, for instance, a method for generating a (32,2) codeand transmitting control information using the (32,2) code will bedescribed.

Example Applied to a (32,2) Code

A control channel format indicator (CFI) indicating the number ofcontrol information among orthogonal frequency division multiplexing(OFDM) symbols in one OFDM frame in 3GPP LTE consists of 2 bits. Sincethe CFI is transmitted through a physical control format indicatorchannel (PCFICH) throughout 16 quadrature phase shift keying (QPSK)symbols, 32 coding bits are needed. Consequently, a code is needed.

Since the performance of a code is proportional to a distance betweencodes, a code having excellent performance has a large distance betweencodes. A code of which distance is maximally separated is called amaximum distance separable (MDS) code. The MDS code may be a simplexcode as an example of a [3,2] code and a Hamming code as an example of a[5,2] code.

A [3,2] simplex code is as follows:

{000, 101, 011, 110}.

In the [3,2] simplex code, it is possible to interchange 0 and 1.Namely, when 0 and 1 are interchanged, the above code set may be used as{111, 010, 100, 001} and the changed code also satisfies acharacteristic of the [3,2] simplex code.

A location of each bit in the [3,2] simplex code is exchangeable. Thishas the same result as a case where each column of the simplex code ischanged in the description with reference to FIG. 4B. In other words,when the first and second bits are exchanged from the above code set, acode set {000,011,101,110} is obtained and this code also has acharacteristic of the [3,2] simplex code.

The [5,2] Hamming code is as follows:

{00000, 01101, 10011, 11110} or {00000, 01011, 10110, 11101}.

It is also possible to interchange 0 and 1 and to exchange a location ofeach bit.

Meanwhile, since it is difficult to directly generate a long code havinga low code rate such as [32,2] code, a method for generating an entirecode by a basic code repeating process as described above is considered.

A basic code uses the [3,2] simplex code. After the basic code isrepeated, a bit part generated because the entire length 32 is not amultiple of 3 may be processed by the following methods, for example, amethod using puncturing as described in the basic embodiment and itsmodification examples, a method using an information bit, and a methodusing the [5,2] Hamming code.

First, a method for repeating the [3,2] simplex code and puncturing onebit will now be described.

According to the exemplary embodiment of the present invention, the[3,2] simplex code is repeated by 11 times and one bit is punctured,thereby generating the [32,2] code.

A puncturing location of one bit may be any location of 33 bits.However, it is desirable that a final code generated by using apuncturing method meets a condition that its minimum distance ismaximized within the Plotkin bound.

The [3,2] simplex code may use a code combination such as {000, 101,011, 110}. This basic code may be used as modified forms as long as aminimum distance property is not varied. For example, there are a methodfor permuting a column and/or a row of a code, a method forinterchanging 0 and 1 of a code, and a method for interchanging 0 and 1of a code and then exchanging a row and/or column of the code.

In repeating the [3,2] simplex code, it is possible to selectively usesimplex codes by 11 times among various [3,2] simplex codes.

Second, a method for repeating the [3,2] simplex code and inserting 2information bits will be described.

According to an exemplary embodiment of the present invention, the [3,2]simplex code is repeated by 10 times and then 2 information bits areadded, thereby generating the [32,2] code.

The locations of the added information bits may be the last part of the[32,2] code. Alternatively, the added bits are positioned at arbitrarylocations among 30 bits. The 2 information bits may be successivelyadded or separately added.

The [3,2] simplex code used for repetition may use a code combinationsuch as {000, 101, 011, 110}. Alternatively, it is possible to usevarious forms within the range of not varying a minimum distancecharacteristic as described above. For example, there are a method forpermuting a column and/or a row of a code, a method for interchanging 0and 1 of a code, and a method for interchanging 0 and 1 of a code andthen permuting a row and/or column of the code.

In repeating the [3,2] simplex code, it is possible to selectively usesimplex codes by 10 times among various [3,2] simplex codes.

Finally, a method for repeating the [3,2] simplex code and adding the[5,2] Hamming code will be described.

In this exemplary embodiment, the [3,2] simplex code is repeated by 9times and then the [5,2] Hamming code is added, thereby generating the[32,2] code.

The added bits of the [5,2] Hamming code are positioned at arbitrarylocations among 27 bits. The 5 bits may be successively added orseparately added.

The [3,2] simplex code used for repetition may use a code combinationsuch as {000, 101, 011, 110}. Alternatively, it is possible to usevarious forms instead of the basic code unless a minimum distancecharacteristic is varied as described above. For example, there are amethod for permuting a column and/or a row of a code, a method forinterchanging 0 and 1, and a method for interchanging 0 and 1 and thenpermuting a row and/or column of the code.

The added [5,2] Hamming code may use any one of the following basiccodes:

{00000, 01101, 10011, 11110},

{00000, 01101, 11011, 10110},

{00000, 10101, 01011, 11110},

{00000, 10101, 11011, 01110},

{00000, 11101, 01011, 10110},

{00000, 11101, 10011, 01110},

{01000, 00101, 10011, 11110},

{01000, 00101, 11011, 10110},

{01000, 10101, 00011, 11110},

{01000, 10101, 11011, 00110},

{01000, 11101, 00011, 10110},

{01000, 11101, 10011, 00110},

{10000, 00101, 01011, 11110},

{10000, 00101, 11011, 01110},

{10000, 01101, 00011, 11110},

{10000, 01101, 11011, 00110},

{10000, 11101, 00011, 01110},

{10000, 11101, 01011, 00110},

{11000, 00101, 01011, 10110},

{11000, 00101, 10011, 01110},

{11000, 01101, 00011, 10110},

{11000, 01101, 10011, 00110},

{11000, 10101, 00011, 01110},

{11000, 10101, 01011, 00110}

It will be understood that the [5,2] Hamming code has a minimum distanceof 3. Since the minimum distance of 3 is equal to a value obtained byadding a minimum distance 2 of the [3,2] simplex code to a minimumdistance 1 of an r-length code, a condition that a minimum distancebetween codes is maximized within the Plotkin bound is satisfied.

In this exemplary embodiment, the [5,2] Hamming code may be used bymodifying the above described basic code while satisfying acharacteristic of the Hamming code. As possible modifications, there area method of changing a code order of the [5,2] Hamming code, a method ofinterchanging 0 and 1 in the [5,2] Hamming code, a method ofinterchanging 0 and 1 in the [5,2] Hamming code and then changing theorder of the code, a method of interchanging locations of bits in theHamming code, a method for interchanging locations of bits in the [5,2]Hamming code and then changing the order of the code, a method forinterchanging 0 and 1 in the [5,2] Hamming code and then interchanginglocations of bits, and a method of interchanging 0 and 1, interchanginglocations of bits, and changing the order of the code.

In repeating the [3,2] simplex code, it is possible to selectively usesimplex codes by 10 times among various [3,2] simplex codes.

Examples of the [32,2] code generated by the above-described methods canbe expressed as follows.

TABLE 1 <0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,0, 1, 1, 0, 1, 1, 0 1, 1, 0, 1> <1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0> <1, 1, 0, 1, 1,0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,0, 1, 1> <0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,>

The above four codes may be generated by one of the following methods.

First, four [32,2] codes shown in Table 1 may be generated by repeatingeach of (0, 1, 1), (1, 0, 1), (1, 1, 0), (0, 0, 0) by 11 times and thenpuncturing the last one bit from the last simplex code. As described inthe above Modification 1, if r=2 and k=2, cases where the first bit ofthe [3,2] simplex code is punctured and the last bit of the [3,2]simplex code is punctured satisfy a condition that the minimum distanceis maximized within the Plotkin bound. Therefore, an optimal code can begenerated.

Second, when the [3,2] simplex codes (0, 1, 1), (1, 0, 1), (1, 1, 0),and (0, 0, 0) are mapped to information bits (0, 1), (1, 0), (1, 1), and(0, 0), respectively as illustrated in FIG. 4C, the [3,2] simplex codes(0, 1, 1), (1, 0, 1), (1, 1, 0), and (0, 0, 0) are repeated by 10 timesand then corresponding information bits are inserted.

Third, four [32,2] codes shown in Table 1 may be generated by repeatingthe [3,2] simplex codes (0, 1, 1), (1, 0, 1), (1, 1, 0), and (0, 0, 0)by 9 times and then adding (0, 1, 1, 0, 1), (1, 0, 1, 1, 0), (1, 1, 0,1, 1), and (0, 0, 0, 0, 0) as the [5,2] Hamming code.

Hereinafter, a method for transmitting control information by using thegenerated [32,2] code will be described.

FIGS. 5A and 5B are diagrams for explaining a process of transmittingcontrol information using a [32,2] code according to an exemplaryembodiment of the present invention.

Information on the number of OFDM symbols occupied by controlinformation among OFDM symbols within one OFDM frame in a 3GPP LTEsystem is transmitted through a PCFICH and the above-described [32,2]code is used. In FIG. 5A, the control information is transmitted over 2OFDM symbols within one OFDM frame. Information on the number of OFDMsymbols occupied by the control information can be expressed by the codeas shown in Table 1.

If the number of OFDM symbols occupied by the control information existsas only 3 cases, then only 3 codes may be used among the 4 codes shownin Table 1.

FIG. 5B illustrates an example using only the first, second and thirdrows among the [32,2] code shown in Table 1 when the control informationoccupies OFDM symbols 1, 2, and 3.

The detailed description of the exemplary embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the exemplary embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims.

Therefore, it will be understood that this patent should not be limitedto the specific embodiments described herein, but be accorded a right tothe broadest scope consistent with the principles and novel featuresdisclosed herein.

The present invention provides a method for generating a long-lengthcode having a low code rate and a method for transmitting controlinformation using the same. These methods may directly be applied to a[32,2] code used for a PCFICH in a 3GPP LTE system. The methods forgenerating a long-length code having a low code rate by repeating andpuncturing a basic code, inserting an information bit, and usingarbitrary codes except for the basic code may variously be applied as amethod for generating a code utilized to transmit specific informationof which error may seriously occur and using the code even incommunication systems except for the 3GPP LTE system.

1. A method for transmitting control information through a downlink by asystem, the method comprising: transmitting the control informationthrough a downlink control channel; and transmitting information on anumber of OFDM (orthogonal frequency division multiplexing) symbolsoccupied by the control information on the downlink control channel byusing a prescribed code, wherein the prescribed code is one of(0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1, 1,0,1),(1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0, 1,1,0),(1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1, 0,1,1), and(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0),according to the information on the number of OFDM symbols occupied bythe control information.
 2. The method according to claim 1, wherein theinformation on the number of OFDM symbols occupied by the controlinformation on the downlink control channel is a control formatindicator (CFI).
 3. The method according to claim 1, wherein theinformation on the number of OFDM symbols occupied by the controlinformation on the downlink control channel is transmitted through aphysical control format indicator channel (PCFICH).
 4. The methodaccording to claim 1, wherein the prescribed code is(0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1, 1,0,1) whenthe number of OFDM symbols occupied by the control information is 1,(1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0, 1,1,0) whenthe number of OFDM symbols occupied by the control information is 2, and(1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1, 0,1,1) whenthe number of OFDM symbols occupied by the control information is
 3. 5.A method for receiving control information through a downlink by a UserEquipment (UE), the method comprising: receiving information on a numberof OFDM symbols occupied by the control information on a downlinkcontrol channel by using a prescribed code; and receiving the controlinformation through the downlink control channel by using the prescribedcode, wherein the prescribed code is one of(0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1, 1,0,1),(1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0, 1,1,0),(1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1, 0,1,1), and(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0),according to the number of OFDM symbols occupied by the controlinformation.
 6. The method according to claim 5, wherein the informationon the number of OFDM symbols occupied by the control information is acontrol format indicator (CFI).
 7. The method according to claim 5,wherein the information on the number of OFDM symbols occupied by thecontrol information is received through a physical control formatindicator channel (PCFICH).
 8. The method according to claim 5, whereinthe prescribed code is(0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1, 1,0,1) whenthe number of OFDM symbols occupied by the control information is 1,(1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0, 1,1,0) whenthe number of OFDM symbols occupied by the control information is 2, and(1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1, 0,1,1) whenthe number of OFDM symbols occupied by the control information is
 3. 9.A method for generating a codeword, the method comprising: acquiringinformation on a number of OFDM symbols occupied by control informationon a downlink control channel; and generating the codeword according tothe acquired information, wherein, in said generating, the codewordgenerated by repeating any one of simplex codes (0, 1, 1), (1, 0, 1),(1, 1, 0), and (0, 0, 0) by 11 times and puncturing a last one bit isused.
 10. A method for generating a codeword, the method comprising:acquiring information on a number of OFDM symbols occupied by controlinformation on a downlink control channel; and generating the codewordaccording to the acquired information, wherein, in said generating, thecodeword generated by repeating any one of simplex codes (0, 1, 1), (1,0, 1), (1, 1, 0), and (0, 0, 0) by 9 times and inserting any one ofHamming codes (0, 1, 1, 0, 1), (1, 0, 1, 1, 0), (1, 1, 0, 1, 1), and (0,0, 0, 0, 0) is used.
 11. A method for generating a codeword, the methodcomprising: acquiring information on a number of OFDM symbols occupiedby control information on a downlink control channel; and generating thecodeword according to the acquired information, wherein the acquiredinformation is expressed as 2 bits information, and, in said generating,the codeword generated by repeating any one of simplex codes (0, 1, 1),(1, 0, 1), (1, 1, 0), and (0, 0, 0) by 10 times and inserting theinformation bits is used.
 12. The method according to any one of claims9 to 11, wherein the acquired information is a control format indicator(CFI).
 13. The method according to claim 12, further comprising:transmitting the codeword through a physical control format indicatorchannel (PCFICH).